Letters : Wrong on rain

Robert Matthews's article is an excellent example of the purely linguistic, as well as mathematical, confusion that can occur when discussing matters of probability ("How right can you be?", 8 March, p 28).

As the premise of his main example he states that "forecasts of rain by the British Meteorological Office are 80 per cent accurate". My interpretation of these words is that if the Met Office forecasts rain it will be right 80 per cent of the time. Matthews, however, interprets them to mean that on 80 per cent of the occasions that rain actually fell the Met Office had made a correct forecast which, as demonstrated in the article, is not at all the same thing.

In fact, to complete his argument Matthews needs an additional assumption that on 80 per cent of the occasions when no rain actually fell the Met Office had also ...

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